Illinois State University Muscular Control of Movement Chapters 17 and 18 Review of Gross Anatomy: l 430 voluntary muscles in the body. l The muscle is

Illinois State University

Muscular Control of Movement Chapters 17 and 18

Review of Gross Anatomy: 430 voluntary muscles in the body. The muscle is

» 75% water, » 20% protein, » and 5% inorganic salts and other

substances.


Types of Muscles:

1. Smooth - blood vessels and organs. 2. Cardiac - heart. 3. Skeletal - movement muscles.


Origins and Insertions

The origin of the muscle is the relatively stable skeletal part to which the muscle attaches. » This is usually more proximal.


Origins and Insertions

The insertion of the muscle is the more mobile skeletal part to which the muscle attaches and is more distal.


Connective Tissue Components


The Structure and Function of Skeletal Muscle

An individual muscle cell is called a muscle fiber.

A muscle fiber is enclosed by a plasma membrane called the sarcolemma.


Sarcolemma


The Structure and Function of Skeletal Muscle:

The cytoplasm of a muscle fiber is called the sarcoplasm.

The extensive tubule network found in the sarcoplasm includes:» t-tubules - allow communication and

transport of substances throughout the muscle fiber

» sarcoplasmic reticulum - which stores calcium.


Sarcoplasm



Myofibrils are composed of sarcomeres, the smallest functional units of muscle.

A sarcomere is composed of filaments of two proteins, which are responsible for muscle contraction.



Myosin is a thick filament, folded into a globular head at one end.

An actin filament is composed of actin, tropomyosin, and troponin.





One end of each actin filament is attached to a z disk.


Sarcomere:

The bands are named according to their optical properties.

The I band (isotropic) - velocity of light is same in all directions. » Contains actin only.


Sarcomere:

A band (anisotropic) - light does not scatter equally. » Contains both actin and myosin.

Z disk (zwischen) - German word for between.



Sarcomere:

H zone - center of A band. » Contains myosin only.


The Sliding Filament Theory:

Muscle action is initiated by a motor nerve impulse.



The action potential travels along the sarcolemma, then through the tubule system, and eventually causes stored calcium to be released from the sarcoplasmic reticulum.




Calcium binds with troponin, and then troponin lifts the tropomyosin molecules off of the active sites on the actin filament, opening these sites for binding with the myosin head.



Once it binds with the actin active site, the myosin head tilts, pulling the actin filament so that the two slide across each other. » The tilting of the myosin head is the power

stroke.





Energy is required before muscle action can occur. » The myosin head binds to ATP, and

ATPase found on the head splits ATP into ADP and Pi, releasing energy to fuel the contraction.



Muscle action ends when the calcium is actively pumped out of the sarcoplasm back into the sarcoplasmic reticulum for storage. » This process, leading to relaxation, also

requires energy supplied by ATP.


Skeletal Muscle and Exercise

Most skeletal muscles contain both ST and FT fibers.



Skeletal Muscle and Exercise:

The different fiber types have different ATPases.

The ATPase in the FT fibers acts faster, providing energy for muscle action more quickly than the ATPase in ST fibers.



FT fibers have a more highly developed sarcoplasmic reticulum, enhancing the delivery of calcium needed for muscle action.



Motor neurons supplying FT motor units are larger and supply more fibers than do neurons for ST motor units.

Thus FT motor units have more fibers to

contract and can produce more force than ST motor units.



The proportions of ST and FT fibers in an individual’s arm and leg muscles are usually quite similar.



ST fibers have high aerobic endurance and are well suited to low-intensity endurance activities.



FT fibers are better for anaerobic activity.

FTa fibers are well utilized in explosive bouts of exercise.



Fiber type is predominantly determined by genetics.

Composition will change over the course of your life as FT fibers atrophy and die.


Classification of Muscle Fibers

Characteristic Type I Type IIa

TypeIIb

Oxidative capacity High Mod. High Low Glycolytic capacity Low High

Highest Contractile speed Slow Fast Fast Fatigue resistant High Moderate Low Motor unit strength Low High High


Characteristics of Muscle Fiber Types

Characteristic ST FTa FTb

Fibers per motor neuron 10-180 300-800 300-800

Motor neuron size Small Large Large Nerve conduction velocity Slow Fast Fast Contraction speed (ms) 110 50 50 Type of myosin ATPase Slow Fast Fast Sarcoplasmic Ret. Dev. Low High High


Motor Units

A motor unit consists of a single motor neuron and all the muscle

fibers it supplies


Neuro-muscular Interaction

Motor units give all-or-none responses.

For a unit to be recruited into activity, the motor nerve impulse must meet or exceed the threshold.

Threshold of excitation.



When this occurs, all muscle fibers in the motor unit act maximally.

If the threshold is not met, no fibers in

that unit act.



More force is produced by activating more motor units, and thus more muscle fibers.



In low-intensity activity, most muscle force is generated by ST fibers.

As the resistance increases, FTa fibers are recruited, and at even higher intensities, the FTb fibers are activated.


Ramping of Muscle Fibers



The same pattern of recruitment is followed during events of long duration.


Muscle Action:

Muscles involved in a movement can be classified as:» agonists (prime movers)» antagonists (opponents or resistors)» synergists (assistants)» fixator, neutralizer, stabilizer


Muscle Action:

The three main types of muscle action are:» concentric, in which the muscle shortens;» static, in which the muscle acts but the joint

angle is unchanged;» eccentric, in which the muscle lengthens.


Generation of Force

The number of motor units activated.» Force production can be increased by

recruiting more motor units.

The type of motor units activated.

The size of the muscle.


Generation of Force:

The muscle’s initial length when activated.» Force production can be maximized if the

muscle is stretched 20% prior to action. » At this point, the amount of energy stored

and the number of linked actin-myosin cross-bridges are optimum.




The angle of the joint.» All joints have an optimal angle at which the

muscles crossing the joint function to produce maximum force.

» This angle varies with the relative position of the muscle’s insertion on the bone and the load placed on the muscle.



The muscle’s speed of action.» Speed of action also affects the amount of

force produced. » For concentric action, maximum force can

be achieved with slower contractions. » The closer you get to zero velocity (static),

the more force can be generated.


Muscle Action:

With eccentric actions, however, faster movement allows more force production.

Concentric

Eccentric


Requirements for Large Muscle Development

Proper nutrition » 65% CHO, 20% Fat, 15% Protein

Resistance Training Genetics Hormonal Secretion Levels

» Testosterone and Androgens


ACSM Strength Guidelines F = 2-3 days per week. I = intensity

» >85% of max for strength,» 50-65% for muscular endurance.

T = duration» 30-90 secs per set, » 8-12 reps, » 1:4 work:rest ratio

S = resistance of any type.


Types of Training

Isometric

muscular tension,

no movement.


Types of Training

Isotonic - muscular tension, movement.» Set resistance» Variable resistance


Types of Training

Isokinetic - muscular tension, speed of movement is controlled.


Strength Training Myths

Strength training will cause “muscle boundness”.

Women who strength train will become masculinized.

Strength training reduces speed. “No pain - No gain”.


Strength Training Myths

It takes hours of training daily to gain muscle mass.

Food supplements will speed up or cause muscle and strength development.

Anabolic steroids are a safe and effective aid.

Documents

Illinois State University Muscular Control of Movement Chapters 17 and 18 Review of Gross Anatomy: l 430 voluntary muscles in the body. l The muscle is